| ID | Name | Type |
|---|---|---|
| #10504 | Oasis Software | P |
| #10505 | Oberon Group | Z |
| #15912 | Oberon International | Z |
| #10506 | Oblique Strategy | ? |
| #10507 | Obo | ? |
| #22763 | Obsolete.gr | - |
| #22489 | Ocean Software France | P |
| #10508 | Ocean Software Ltd | P |
| #10509 | Ocean-Imagine Hellas | Z |
| #10510 | Octavio Campos Barroso | + |
| #10511 | Octavio Montagud Ballester | + |
| #10512 | Octocon Data | ? |
| #15913 | Octogram | ? |
| #17582 | Octopus Computing Holidays | C |
| #10513 | Octopus Software | Z |
| #22000 | Odd Job | + |
| #22211 | Oddball Software | P |
| #10514 | Oddworld Inhabitants Inc | Z |
| #10515 | Odin Computer Graphics Ltd | P |
| #10516 | Odisea Software | Z |